Platelet Transfusion Thresholds

No single platelet count applies to every patient. The threshold depends on why the count is low, whether the patient is bleeding, what procedure is planned and whether platelet function is also impaired. Prophylactic platelets in a stable patient give small benefit, add risk and use a scarce product, so thresholds are deliberately low for prophylaxis and higher for bleeding or procedures.

Principle. The count is one input. Decide with bleeding, fever, sepsis, rate of fall, coagulopathy, drugs affecting platelet function and the procedure.

Risk context. Unnecessary platelet transfusion causes reactions, bacterial infection, alloimmunisation and refractoriness, and wastes stock. Under-treatment causes preventable bleeding, particularly in the brain, eye and airway.

Special groups. Neonates, children, pregnancy, liver disease, malignancy and stem cell transplant, antiplatelet therapy, and acute promyelocytic leukaemia.

Usual adult thresholds, each with its circumstances.

Platelet function disorders. A normal count with antiplatelet drugs, uraemia or cardiopulmonary bypass is not a threshold problem. Platelets are given for bleeding only. Platelet transfusion is not advised for spontaneous intracranial haemorrhage in patients on antiplatelet drugs unless a neurosurgical procedure is planned, because it may be harmful.

Where platelets are not indicated. Immune thrombocytopenia, thrombotic thrombocytopenic purpura and heparin induced thrombocytopenia without life-threatening bleeding, dengue without significant bleeding, and stable chronic thrombocytopenia.

Differential considerations. Spurious thrombocytopenia (clumping in EDTA, repeat in citrate), drug causes, and consumption.

Red flags. Headache, visual change, haematuria, melaena, extensive mucosal bleeding and falling count over hours.

Plan.

1. Confirm the count on a valid sample.

2. Decide the setting and threshold.

3. Order one adult dose, with ABO identical product where possible.

4. Transfuse shortly before the procedure, not hours earlier.

5. Check the count 10 minutes to 1 hour after, to confirm the target was reached.

6. Reassess bleeding and repeat only for a defined reason.

Therapeutic platelets in active bleeding. Give early in massive haemorrhage, and keep the count over 50 x 10⁹/L (over 100 x 10⁹/L in central nervous system bleeding), reassessing every 30 to 60 minutes.

Alternatives. Tranexamic acid, local haemostasis, desmopressin for platelet function disorders such as uraemia, and treatment of the cause.

Special groups.

• Liver disease: count and viscoelastic results guide use, and prophylaxis before low risk procedures is not usually needed.

• Pregnancy: counts over 50 x 10⁹/L for caesarean section and about 70 to 80 x 10⁹/L for neuraxial anaesthesia.

• Haematology and stem cell transplant: prophylaxis at under 10 x 10⁹/L, higher with risk factors.

Monitoring. Platelet count before and 10 minutes to 1 hour after transfusion, bleeding, and vital signs during transfusion.

Complications. Reactions, bacterial contamination, transfusion related acute lung injury, overload, alloimmunisation and refractoriness.

Referral and escalation. Haematology for poor increments, unexplained thrombocytopenia and procedures in high risk patients. Neonatologist for thresholds in infants.

Disposition. Record the threshold used and the reason for any deviation. Arrange a repeat count and plan to treat the cause of thrombocytopenia.